The present invention relates to transmission shift mechanisms and particularly to brake-transmission shift interlocks (BTSI) therefor.
Brake transmission shift interlocks (BTSI) are well-known, and prevent an automobile transmission from being shifted from the park position without the brake pedal first being depressed. BTSI prevents accidental movement of the vehicle. U.S. Pat. Nos. 5,647,465 and 6,945,377, and US Patent Application Publication No. 2005-0236252-A1, the complete disclosures of which are incorporated herein by reference, describe various embodiments of such devices.
BTSI typically provide a solenoid that serves as a park position unlocking device, which permits shifter movement from the park position only under certain conditions. The solenoid has an armature which is normally extended as by the biasing force of a spring, and which is retracted from its normal (unpowered) position when activated in response to a signal indicating that moving the shifter from the park position is permissible.
In the solenoid's extended position, an inhibitor connected to the armature is positioned such that the shift lever pawl is blocked from being removed from the park detent in the shifter gate. Shifting from the park position is thus prevented. An example of an existing BTSI is shown in FIG. 1, wherein shifting the transmission out of the park position will move the shift lever pawl 210 upwards and into contact with the inhibitor 212 rigidly attached to or integrally formed with the solenoid armature 214. Lateral movement of the inhibitor 212 is restricted by a travel stop 216 provided on the shifter bracket. Movement of the pawl 210 out of the park detent and into the shift gate 222, wherein it can be moved to the reverse and other shifter positions, can only occur once the solenoid armature 214 has been retracted, and the inhibitor 212 thus removed from the path of the pawl 210 as it moves towards the travel stop 216.
FIG. 2 shows one example of a solenoid 240 employed in existing BTSI. Referring now to FIG. 2, the solenoid includes a metal container 232 and a coil 234 enclosing a portion of the armature 214. In current solenoids used for BTSI, the inhibitor 212 and solenoid armature 214 are of a coupled design whereby lateral forces F exerted on the inhibitor are also exerted on the solenoid armature 214. These solenoids also typically have plastic inserts or bushings 230 used for noise dampening, and to provide an armature location and guidance system. Such coupled BTSI solenoids are sensitive to side loading and cannot withstand the shear side loading imparted on the inhibitor 212, and thus on the armature 214, by the shift lever pawl 210 when its movement from the park detent is opposed during BTSI operation. A BTSI solenoid having an inhibitor that can withstand high compressive loads while not subjecting the armature to potentially damaging high shear loads, whereby solenoid damage can be avoided, is desirable. Such an inhibitor may be characterized as a decoupled inhibitor.
A further problem with some previous BTSI is that the park position detection switch and the BTSI are coupled by design, and rely on the same axial motion to engage each device. Such BTSI require more travel of the link between the solenoid and the park switch to accommodate dimensional stackups of the assembled components and to satisfy the functional requirements of the BSTI system. Thus, a park position switch decoupled from, and which reacts to a motion other than, the BTSI solenoid armature motion when shifting into the park position is desirable, wherein engagement of such a decoupled park position switch is independent of the BTSI solenoid function.